Power control in a wireless network

ABSTRACT

A network device may select a value of a multi-level transmit power control (TPC) command from a plurality of pre-defined values. The network device may transmit on a single channel an allocation of an uplink resource and the multi-level TPC command.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/645,523, filed Jul. 10, 2017, which is a continuation of U.S. patentapplication Ser. No. 15/229,906, filed Aug. 5, 2016, which is acontinuation of U.S. patent application Ser. No. 14/713,719, filed May15, 2015, which issued as U.S. Pat. No. 9,414,326 on Aug. 9, 2016, whichis a continuation of U.S. patent application Ser. No. 13/727,153, filedDec. 26, 2012, which issued as U.S. Pat. No. 9,055,586 on Jun. 9, 2015,which is a continuation of U.S. patent application Ser. No. 10/917,968,filed Aug. 12, 2004, which issued as U.S. Pat. No. 8,897,828 on Nov. 25,2014, which are both incorporated by reference as if fully set forth.

This application is related to U.S. patent application Ser. No.13/726,976, filed Dec. 26, 2012, which issued as U.S. Pat. No. 8,983,522on Mar. 17, 2015.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to power control in a mobile radio system orwireless communication system, and more particularly, to controllingreceived power levels in a code division multiple access (CDMA) radiosystem.

2. Description of the Prior Art

Typically, radio signals transmitted with increased power result infewer errors when received than signals transmitted with decreasedpower. Unfortunately, signals transmitted with excessive power mayinterfere with the reception of other signals sharing the radio link.Wireless communication systems employ power control schemes to maintaina target error rate of a signal received on a radio link.

If a received signal includes a rate of errors far above a target errorrate, the received signal may result in an undesirable effect on adelivered service. For example, excessive errors may lead to brokenvoice during voice calls, low throughput over data links, and glitchesin displayed video signals. On the other hand, if the received signalincludes a rate of errors well below the target error rate, the mobileradio system is not efficiently using its radio resources. A very lowerror rate may mean that a signal is transmitted with an excessive levelof power and that user could be provided a higher data rate.Alternatively, if the power level of a signal is sufficiently reduced,additional users may be serviced. If data rates are increased, a usermay receive a higher level of service. Therefore, if a target error ratefor each user is met within a tolerance threshold, a radio resource maybe more optimally used.

A wireless communication system often employ one of either an open loopscheme or a closed loop scheme to control uplink transmit power of amobile radio. Uplink typically refers to the radio link from a mobileradio to a base station, where as the downlink typically refers to thelink from the base station to the mobile radio. A mobile radio is notnecessarily mobile and may also be referred to as a mobile, a user, userequipment (UE), a terminal or terminal equipment. A base station mayalso be referred to as a Node-B.

The error rate is related to a received signal tonoise-plus-interference ratio (SNIR); a higher SNIR generally results ina lower error rate; and conversely, a lower SNIR generally results in ahigher error rate. The exact relationship between SNIR and error rate,however, is often a function of several factors including radio channeltype and the speed at which a mobile is travelling.

A target error rate is often reached using a two stage process, whichincludes an outer loop and an inner loop. A first process may operate asan outer loop and may be tasked to adjust a target received SNIR (SNIRTarget). This first process tracks changes in the relationship betweenSNIR and error rate. The outer loop sets an SNIR Target that isgenerally used several times by the inner loop. Periodically, the outerloop may adjust or update this SNIR Target used by the inner loop. Forexample, if an actual error rate exceeds a desired error rate, the outerloop may increase the value of the SNIR Target.

A second process operates as an inner loop and tries to force the linkto exhibit the SNIR Target determined by the outer loop. The inner loopmay operate by closed loop or by open loop means.

In the open loop method of the inner loop process, a UE uses an SNIRTarget value that is derived by the network and signalled to the UE. Theinner loop running in the UE attempts to maintain the SNIR Target. TheUE uses the information signalled to it and monitors the receivedstrength of signals it receives to determine a power level at which itwill transmit. Advantageously, this open loop method compensates forfast channel fading by determining the path loss on a per frame basesand by adjusting the transmit power accordingly. Unfortunately, thisopen loop method is relatively slow at compensating for changes due tointerfering signals from other transmitters.

In the closed loop method of the inner loop process, a closed loopscheme operates to match an SNIR Target. A received SNIR measurement ismade by the network on an uplink signal. The SNIR measurement iscompared within the network to the SNIR Target value. The inner loopdrives the system to match the SNIR Target by issuing transmit powercontrol commands from the network to a UE. The commands instruct the UEto increase or decrease its transmitted power by a predetermined step dBamount. Unfortunately, such closed loop methods demand a very highcommand update rate to adequately compensate for fast channel fadingbecause of the single-dB-step commands used. At slower update rates,fast channel fading is not tracked adequately since a large number ofiterations and long delays are needed to compensate for a change inpower that is substantially larger than the dB-step value.

Both the closed loop scheme and the open loop scheme have theirdisadvantages. Therefore, an improved method and system are needed thatbetter balances the conflicting goals of reducing errors in a receivedsignal while also reducing interference imposed on signals received atother receivers. An improved method and system are also needed to betterreduce the overall residual SNIR fluctuations experienced by each userssignal at a receiver.

BRIEF SUMMARY OF THE INVENTION

Some embodiments provide a method of power control in a radiocommunications system, the method comprising: determining a path loss ofa radio channel between a base station and a remote transceiver;receiving a transmit power control (TPC) command transmitted to theremote transceiver from the base station; and calculating a transmitpower level for the remote transceiver based on the path loss and theTPC command.

Some embodiments provide a method of power control in a radiocommunications system, the method comprising: receiving a signal at asecond transceiver transmitted from a first transceiver; measuring apower level of the received signal; receiving a transmit power control(TPC) command at the second transceiver transmitted from the firsttransceiver; and calculating a transmit power level for the secondtransceiver based on the power level of the received signal and the TPCcommand.

Some embodiments provide a method of uplink power control in a CDMAradio communications system, the method comprising: receiving an uplinksignal; determining an error metric of the uplink signal; updating anSNIR target based on the error metric; measuring a received SNIR of theuplink signal; comparing the measured received SNIR with the SNIRtarget; assigning a first value to a step indicator if the measuredreceived SNIR is greater than the SNIR target, and assigning a secondvalue to a step indicator if the measured received SNIR is less than theSNIR target; transmitting a transmit power control (TPC) commandinstructing a transmitter to adjust an uplink transmit power level basedon the step indicator; receiving the TPC command including the stepindicator; accumulating the step indicator value; broadcasting adownlink signal including an indication of a downlink power level,wherein the signal is transmitted at the downlink power level; measuringthe received power of the downlink signal; and setting a transmit powerlevel base on the received power level, the indication of the downlinkpower level, and the accumulated step indicator value.

Some embodiments provide a method comprising: measuring a power level ofa received signal; receiving a transmit power control (TPC) command; andcalculating a transmit power level based on the power level of thereceived signal and the TPC command.

Some embodiments provide a radio comprising: a receiver including anoutput to provide a measured received power level; an accumulator havingan input for accepting step increase and decrease instructions and anoutput providing a sum of past step instructions; a power level settingcircuit coupled to the accumulator output and coupled to the receiveroutput, wherein the power level setting circuit sets a transmit powerbases on the accumulator output and the measured received power level;and a transmitter, wherein the transmitter transmits a signal at the settransmit power.

Other features and aspects of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings which illustrate, by way of example, the featuresin accordance with embodiments of the invention. The summary is notintended to limit the scope of the invention, which is defined solely bythe claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a wireless communication system.

FIG. 2 illustrates a wireless communication system using an open loopscheme.

FIG. 3 illustrates a wireless communication system using a closed loopscheme.

FIG. 4 illustrates a wireless communication system using elements ofboth open loop and closed loop schemes, in accordance with the presentinvention.

FIGS. 5A, 5B and 5C each illustrate a simulated probability densityfunction of the received SNIR in the network.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, reference is made to the accompanyingdrawings which illustrate several embodiments of the present invention.It is understood that other embodiments may be utilized and mechanical,compositional, structural, electrical and operational changes may bemade without departing from the spirit and scope of the presentdisclosure. The following detailed description is not to be taken in alimiting sense, and the scope of the embodiments of the presentinvention is defined by the claims of the issued patent.

Some portions of the detailed description which follows are presented interms of procedures, steps, logic blocks, processing, and other symbolicrepresentations of operations on data bits that can be performed oncomputer memory. A procedure, computer executed step, logic block,process etc., are here conceived to be a self-consistent sequence ofsteps or instructions leading to a desired result. The steps are thoseutilizing physical manipulations of physical quantities. Thesequantities can take the form of electrical, magnetic, or radio signalscapable of being stored, transferred, combined, compared, and otherwisemanipulated in a computer system. These signals may be referred to attimes as bits, values, elements, symbols, characters, terms, numbers, orthe like. Each step may be performed by hardware, software, firmware, orcombinations thereof.

FIG. 1 shows a block diagram of a wireless communication system. Anetwork 100 may include one or more base station controllers 110, suchas a radio network controller (RNC), and one or more base stations 120and 130, such as a Node-B, wherein each Node-B is connected to an RNC.The network 100 communicates with one or more users 140, 150 through achannel 160, also referred to as a radio link, created between a basestation and a user.

Two mechanisms are primarily responsible for changes in the SNIR of asignal travelling through a radio link.

First, changes in the channel affect the SNIR. The instantaneous pathloss between a base station and a user may vary as the user changesposition or the user's environment changes. Rapid changes may occur as aresult of a transmitted signal combining constructively anddestructively as the signal travels along multiple paths from a basestation and to the user. Additionally, slower changes may occur due toattenuation of the radio waves with increased distance between the basestation and the user. Slower changes may also occur due to signalobstruction by buildings, vehicles and hills.

Second, signals from other transmitters affect the SNIR. For example,signals intended for other mobile radios or other base stations mayincrease interference in the radio link and thus reduce a receivedsignal's SNIR.

In Time Division Duplex (TDD) systems, both uplink and downlink sharethe same carrier frequency. Due to this reciprocity in the links, pathloss measurements made on the downlink by a mobile radio may be usedestimate the path loss on the uplink. That is, a measured downlink pathloss may be used to estimate the uplink path loss. The estimated uplinkpath loss will be less reliable with the passing of time but may beadequate within a frame period. Therefore, a mobile radio may determinea transmit power level for an uplink transition that compensates for anestimated uplink path loss, thereby providing a received signal to abase station at an expected input power level.

Downlink path loss measurements may be facilitated by a beacon channel,which is transmitted from a base station at a reference power level. Amobile radio is informed of the actual transmit power level being usedby the base station for the beacon channel. In addition to knowing theactual transmit power level of a beacon channel, the mobile radio maymeasure a received signal power level. By measuring the received signalpower level, the mobile radio can compute a downlink path loss as thedifference between the actual transmit power level and the receivedsignal power level. Thus, the mobile radio is able to estimate theuplink path loss in a channel between the base station and the mobileradio and properly set its uplink transmit power level.

The path loss calculation may be updated as often as a beacon signal istransmitted and received. In a UTRA TDD system in compliance with thethird generation partnership project (3GPP) specifications, a beaconsignal is transmitted either once or twice every 10 milliseconds (ms).If an uplink transmission follows a beacon transmission within arelatively short period of time, a mobile radio can compensate for thefast fluctuations (fast-fading) in a radio channel. Such is the case formobiles travelling at slow to moderate speeds if a beacon signal istransmitted either once or twice every 10 ms and the uplinktransmissions occur in the intervening period.

Additionally, a radio channel may be adversely affected by changes ininterference levels over time. These temporal interference changes maybe accommodated by a base station, measuring and communicatinginterference levels seen in each uplink timeslot. In a UTRA TDD system,a table having values of the measured interference for each timeslot maybe broadcast to all users via a Broadcast Channel (BCH). The broadcastedinformation may be updated approximately every 16 frames (160 ms)depending upon the system configuration. In other embodiments, a mobileradio may receive this interference table as a signalled messagedirected to the individual mobile radio.

The 3GPP specifications describe two separate schemes for power controlof uplink channels: an open loop scheme and a closed loop scheme. Forexample, in 3GPP 3.84 Megachips per second (Mcps) TDD systems, open looppower control is specified for all uplink channels. In 3GPP 1.28 McpsTDD systems, open loop power control is specified only for physicalrandom access channels (PRACH). Also defined by 3GPP is animplementation of a closed loop power control scheme. For example, see3GPP recommendations for UTRA TDD systems operating at 1.28 Mcps fornon-PRACH uplink channels.

In a wireless communication system using an open loop scheme, a networkand UE use an outer loop to update and signal to the UE an SNIR Targetvalue, thereby influencing the UE's transmit power. The network updatesthe SNIR Target value to be signalled based upon an observed error rateon the uplink. Once received, the mobile radio takes into account thesignalled SNIR Target value when deriving a transmit power level that itwill apply to the next uplink signal transmitted.

In a 3GPP 3.84 Mcps system incorporating an open loop scheme, a networkinstructs the UE with an SNIR Target value. The network also signals itsbeacon transmit power level and may also provide a measure of uplinkinterference for each timeslot as measured by the network. The UEreceives an input signal that is typically a combination of attenuatedversions of the network signal, which passed through a radio channel,along with interfering signals from other transmitters. The UE measuresthe received power level of the attenuated network signal and determinesa path loss of the radio channel. The UE also decodes the signalled SNIRTarget value from the network signal. The UE computes a transmit powerlevel based on the SNIR Target value, the determined path loss and, ifavailable, the uplink interference measurements.

FIG. 2 illustrates a wireless communication system using an open loopscheme. A UE transmits 200 user data at a determined transmit powerlevel. An uplink signal 202, which includes user data 204, propagatesthrough the radio link. The network receives an attenuated version ofthe transmitted signal. The network measures 207 an uplink interferencevalue and determines 206 an error metric of the uplink signal. Thenetwork may use the measured uplink interference value to update 208 aninterference measurement table. The interference measurement table mayinclude average measured interference levels for each uplink timeslot.

The network also uses the error metric to update 210 an SNIR Targetvalue. The network transmits 212 SNIR Target in a signalling message onthe downlink 214, which includes the SNIR Target 216. The UE receivesand saves 220 the SNIR Target. The network also broadcasts 222 a beaconsignal on the downlink 224. The downlink 224 propagates the signal,which includes an indication of the beacon power level 226, over theradio link. The network may also broadcast the interference measurements228. The UE measures 230 the received power level and saves 232 theinterference measurements for later processing.

With the measured power level and the signalled beacon power level, theUE may determine a path loss. The UE may use the saved received SNIRTarget 216, the saved received interference measurements 228 and thecomputed path loss to set 234 a transmit power level. This transmitpower level may be used by transmitter 200 to set the power level oftransmitted user data 204 on the uplink 202.

The 3GPP specifications also define a closed loop scheme. For example, a3GPP 1.28 Mcps system employs a closed loop scheme using an outer loopand an inner loop. The closed loop TPC scheme is the primary powercontrol mechanism used for all non-PRACH channels in a 1.28 Mcps TDDsystem. The closed loop TPC scheme is not currently employed for theuplink of 3.84 Mcps TDD systems.

The outer loop determines an SNIR Target value and the inner loop usesthe SNIR Target value. The outer loop includes network components thatdetermine an error metric, such as a bit error rate, a block error rateor a CRC error count, on uplink traffic from UEs. This error metric isused to set and update an SNIR Target value. An inner loop includesnetwork components that use the SNIR Target value computed and set bythe outer loop. The network measures a received SNIR value of the uplinksignal.

Next, a comparator determines whether the measured SNIR value is greaterthan or less than the SNIR Target value. If the measured SNIR value isgreater than the SNIR Target value, the network signals a transmit powercontrol (TPC) command on the downlink instructing the UE to reduce itscurrent transmitter power by a step value (e.g., 1 dB). On the otherhand, if the measured SNIR value is less than the SNIR Target value, thenetwork signals a TPC command instructing the UE to increase its currenttransmitter power by the step dB value.

In a system employing only a closed loop power control scheme, severalTPC commands may be necessary to properly bring the UE's transmittedpower in line with the SNIR Target value. For example, if a path lossincreases from one frame to the next by 15 dB, the system will take 15TPC commands to compensate for the 15 dB fade. A UE accumulates theincrease and decrease TPC commands to determine a proper uplink transmitpower level. By increasing and decrease uplink power levels of each UE,a network attempts to control the power level of each UE such that theratio of the received uplink energy level per transmitted bit to thespectral density of the noise and interference signals is a constantvalue. This TPC command adjustment process is performed for each UE in acell. The constant value, however, may be non-uniform among the UEsdepending upon the configuration of the system.

In a closed loop TPC scheme, the inner loop SNIR is maintained via aclosed loop method using binary feedback. The feedback indicates eitherpower up or power down. Every time a TPC command is received anintegrator in the UE is used within the inner loop to update the UEtransmit power by a step amount +/−Δ dB. The TPC commands themselves arederived by the network and are signalled to the UE via a downlinkchannel. When calculating the proper TPC command to send, the networkmeasures the received SNIR and compares this measured value to an SNIRTarget value. If the SNIR is too low, an up command is sent. If the SNIRis too high, a down command is sent. The target SNIR value is updated bythe outer loop based upon the observed error performance of the link. Inthis way, both the inner and outer feedback loops are closed by the TPCsignalling.

FIG. 3 illustrates a wireless communication system using a closed loopscheme. The closed loop scheme includes an outer loop in which a UEtransmits 300 user data over the radio link in an uplink signal 302 thatcontain the user data 304. The network determines 306 an error metric ofthe received uplink signal. Using the error metric, the network computesand updates 308 an SNIR Target value.

The closed loop scheme also includes an inner loop in which the networkmeasures 310 the received SNIR of the uplink signal 302. The networkcompares 312 the measured SNIR with the SNIR Target determined in theouter loop. The inner loop generates and transmits 314 a TPC commandbased on the comparison 312. A downlink signal 316 carries the TPCcommand 318 over the radio link. The UE accumulates 320 the TPC commandsand uses the accumulated TPC commands to set 322 a transmit power forfuture uplink transmissions 300.

A mobile radio system employing either an open loop scheme or a closedloop scheme has its advantages and disadvantages.

The open loop scheme advantageously adapts quickly to path loss changes.If the path loss is observed to have worsened, for example by 15 dB inone 10 ms interval, the transmit power may be adjusted accordingly. Afurther advantage is that the open loop may continue to be partiallyupdated in the absence of user-specific feedback signalling. Forexample, when a UE does not receive updated SNIR Target values, theouter loop pauses but changes in the path loss may continue to betracked.

Disadvantageously, the timeslot interference level update rate in anopen loop system is relatively slow. Therefore, a system using an openloop scheme is slower to adapt to interference changes than a systemusing the closed loop scheme. A further disadvantage of the open loopscheme is that interference is considered to be the same for all UEs ina particular uplink timeslot. That is, each UE assigned to a timeslotuses the same interference measurement signalled by the base station onthe BCH. A commonly used interference measurement table makesassumptions about the statistical nature of the interference and doesnot consider the individual cross-correlation properties of the uplinkchannelization codes. It is thus left to the outer loop to compensatefor these effects, but unfortunately on a slow basis.

Conversely, the closed loop only scheme is less able to adapt to fastpath loss changes because the closed loop can only move by a step A dBduring each update. Thus, if the path loss has changed between updatesby 15 dB and the step A dB value is only 1 dB, the closed loop is notable to adjust quickly since it can move only by 1 dB during each cycle.Therefore, for the same update rate (e.g., once per 10 ms), a closedloop TPC scheme is less able to track the fast fading observed in commonmobile radio channels. Furthermore, the closed loop may not be updatedduring a pause in transmission of the TPC commands.

Advantageously, the closed loop is relatively quick to respond to uplinkinterference changes since both path loss and interference areaccommodated by the same loop. The closed loop scheme using TPC commandshas a further advantage in that it allows for per-user interferenceadaptation, in contrast to the open loop scheme, which broadcasts anaverage interference table for each timeslot.

In accordance with the present invention, aspects of both an open loopscheme and a closed loop scheme are strategically combined to form apower control method. Some embodiments of the present inventionadvantageously combine elements of both open loop and closed loopschemes to control power levels, thereby avoiding one or more of thedisadvantages associated with either of the separately used schemes.

In accordance with some embodiments of the present invention, a UEincorporates the TPC structure of a closed loop scheme and the path lossestimation structure of an open loop scheme. Some embodiments of thepresent invention allow for both relatively quick adaptation to fastfading and also allow for per-user interference adaptation, and retainthe ability to partially update the power control loop even in thetemporary absence of TPC commands.

Some embodiments of the present invention require modifications to oneor more elements of a standard mobile radio system. For example, someembodiments require changes to just a UE, while other embodimentsrequire modifications to just the network. Embodiments that modify a UEbut not the network allow the UE of the present invention to operatewith legacy base stations. Similarly, embodiments that modify thenetwork but not the UE allow the network of the present invention tooperate with legacy UEs. Still other embodiments of the presentinvention require modification to both the network and the UE.Embodiments modifying standard network elements may include changes tojust a base station but not a radio network controller (RNC). Otherembodiments modify both a base station and an RNC.

Some embodiments of the present invention, incorporate a loop havingthree components: an open loop component located in the UE, an SNIRcomparison loop located in the network, and an SNIR update componentalso located in the network.

First, an open loop component may be located in the UE and driven bymeasured beacon received power levels and path loss calculations. Thisloop tries to adapt to all instantaneous path loss changes on aper-beacon transmission basis. The partial power calculated by this loopis a function of the beacon signal transmission power (P_(Tx)) and thebeacon received signal code power (RSCP) and is denoted P_(open)(k),where k represents the current frame number. P_(Tx) is known to the UEand derived from the base station signalled power level (428, FIG. 4)and the measured power level for frame k, (RSCP(k)), may be determinedby the UE receiver (432, FIG. 4). P_(open)(k) may also be a function ofa constant value (C) to ensure that the transmission arrives at anappropriate power level.P _(open)(k)=P _(Tx)−RSCP(k)+C

Second, an SNIR comparison loop is located in the network, such as inthe Node-B. The SNIR comparison loop is driven by received SNIR metrics.A received SNIR is compared to a SNIR Target value, which is set by anouter loop. A comparison result leads to the signalling of a TPC commandthat is signalled to the UE to change its transmit power. Binarysignalling may be used, such that the TPC command indicates a change intransmission power by a fixed amount either up or down. Alternately, amulti-level TPC command may be used.

Third, an outer loop is located in the network, such as in the Node-B orRNC. The outer loop is driven by the data error statistics observed onthe uplink transmissions. The outer loop is responsible for setting anSNIR Target level for the SNIR comparison loop.

An optional auxiliary process in the UE adjusts the transmit power basedupon: (a) y_(SF), the spreading factor (SF) of the physical channel; and(b) β_(TFC), the selected transport format (TFC).

Thus, for the current frame k, the UE may calculate the transmit powerP_(Tx)(k) as shown below where K is the initial frame number determinedwhen the power control process begins; TPCi is −1 for a down TPCcommand, +1 for an up TPC command and 0 if no TPC command is received;and step is the magnitude of the amount added to an accumulator uponreceipt of each TPC command. The transmit power P_(Tx)(k) may be updatedfor every frame period. Alternatively, the transmit power P_(Tx)(k) maybe updated each time a new TPC command is received. Alternatively, thetransmit power P_(Tx)(k) may be updated only when either a TPC commandor a new power level is received from the network.P _(Tx)(k)=P _(open)(k)+step·Σ_(i=k−K) ^(k)TPC_(i) +y _(SF)+β_(TFC)

An embodiment of a power control scheme, in accordance with the presentinvention, is shown diagrammatically in FIG. 4. The y_(SF) and β_(TFC)adjustment factors are not shown for diagrammatical clarity.

FIG. 4 illustrates a wireless communication system using elements ofboth open loop and closed loop schemes, in accordance with the presentinvention. A UE transmits 400 user data at a determined transmit powerlevel. An uplink signal 402, which includes the user data 404,propagates through the radio link. The network receives an attenuatedversion of the transmitted signal.

The network determines 406 an error metric of the uplink signal 402.Optionally, the network measures an uplink interference level and mayupdate 422 an interference measurement table. Data measured or computedfrom uplink measurements may be entered into the interferencemeasurement table. The interference measurement table may includeaverage measured interference levels for each uplink timeslot. Withinthe network the error metric may be used to update 408 an SNIR Targetvalue.

The network also transmits 424 a beacon signal. The downlink signal 426,which includes an indication of the beacon transmit power level 428,propagates over the radio link. Optionally, the network may broadcastthe interference measurements 430. The UE saves 432 the signalled powerlevel, measures the received power level and, if available, saves 434the interference measurements for later processing.

As in a closed loop scheme, a UE transmits 400 user data over the radiolink in an uplink signal 402 that contain the user data 404. The networkdetermines 406 an error metric of the received uplink signal. Using theerror metric, the network computes and updates 408 an SNIR Target value.

The network also measures 410 the received SNIR of the uplink signal402. The network compares 412 the measured SNIR with the determined SNIRTarget. The network generates and transmits 414 a TPC command based onthe comparison 412. A downlink signal 416 carries the TPC command 418over the radio link. The UE accumulates 420 the TPC commands and usesthe accumulated TPC commands in part to set 436 the transmit power levelfor future uplink transmissions 400.

As in an open loop scheme, with the measured power level and thesignalled beacon power level, the UE may determine a path lossP_(open)(k). The UE may use the saved received interference measurementsI(k) to adjust the transmission power following a pause in transmissionor following a pause in receipt of TPC commands. The UE may use theaccumulated TPC commands

$\sum\limits_{i = {k - K}}^{k}{TPC}_{i}$the computed path loss P_(open)(k), adjustment factors y_(SF) & β_(TFC)and optionally, adjustments based upon I(k) to set 436 a transmit powerlevel. This transmit power level P_(Tx)(k) may be used to set the uplinkpower level of transmitted 400 user data on the uplink 402.

The downlink signal 426, which contains the power level 428 and maycontain the interference measurements 430, is broadcast in a cell.Previous UEs using a closed loop scheme do not use measurements of thedownlink received power while monitoring the power level signalling in abeacon broadcast to set the uplink transmission power. Similarly,previous UEs using a closed loop scheme do not compute or do not usecomputations of the downlink path loss while processing TPC commands. Aprevious UE simply follows the TPC commands as it is instructed to setits transmit power level. If a network instructs a known UE to increaseits transmit power by one step amount, the previous UE shall increaseits power level by one step amount.

In accordance to the present invention, a UE may receive a TPC commandinstructing it to change its transmit power by one step level in aparticular direction, but the UE may actually change its transmit powerlevel by a different amount or in fact an amount in the oppositedirection. The UE uses the TPC only as a factor in determining whetherto increase transmit power level, decrease transmit power level or leavethe transmit power level unchanged.

For example, assume a UE just transmitted a burst to a Node-B at 20 dBmover a radio link with a path loss of 110 dB. The received power at theNode-B receiver would be −90 dBm, which is the difference between 20 dBmand a loss of 110 dB. Next, assume the Node-B wants to receive an uplinksignal from the UE at −89 dBm. The Node-B would signal and the UE wouldreceive a TPC command instructing the UE to increase the uplink transmitpower level by 1 dB. Also assume that the path loss improves from theprevious frame to this frame by +10 dB (e.g., from 110 dB to 100 dB).

A previous UE would transmit the next burst at +21 dBm, which is the sumof the previous level (+20 dBm) and the step increase (1 dB). Thetransmitted +21 dBm signal would probably reach the Node-B at −79 dBm, asignal level that is +10 dB too great because the channel improvementwas not taken into account.

In accordance with the present invention, a UE would account for the newpath loss.

The previous transmit power level of +20 dBm would be decreased by +10dB to account for the improved channel path loss of +10 dB. Theresulting transmit power level would then be +10 dBm. The UE alsoaccounts for the TPC command by adjusting the transmit power level bythe desired step of +1 dB, resulting in a new transmit power level of+11 dBm, which both accounts for the improved channel (+10 dB) andaccommodates the Node-B's desire to have a received signal with a stepincrease (+1 dB). The +11 dBm would reach the Node-B at the desiredlevel of −89 dBm if the channel pathloss estimate was accurate. As shownin this example, the transmit power level dropped 9 dB (from +20 dBm to+11 dBm) even though the Node-B TPC command instructed an increase of 1dB.

Therefore, even though a UE receives a network TPC command instructingit to step up or down its uplink transmit power by 1 dB, the UE mayactually change the transmit power level by a different amount. In fact,the UE transmit power level may change in a direction opposite of theTPC command as exemplified above.

During a period of inactivity on the uplink 402, TPC commands 418 maynot have been received by the UE. The UE transmit power level for asubsequent initial transmission 400 may be determined using currentupdates of the open loop component. That is, the initial transmit powerlevel may be determined based on the beacon power level 428, themeasured 432 received power level, and optionally the interferencemeasurements 430. The open loop component does not require feedback,thus may continue to be updated every beacon transmission even duringthe uplink transmission pause.

The history stored in the TPC accumulator may be stale. In somecircumstances the history may be considered useful and is not reset.Alternatively, the accumulated TPC history could be used to set theuplink transmit power level but with some excess power margin added toensure a clean start to the loop. Alternatively, the UE may decide todiscard the accumulated TPC history and to reset it to a default orinitial value. The default or initial value may optionally be based upona received interference measurement table 430.

The ability of the open loop component to compensate for fast fading isa function of the channel speed and the delay between the beacontimeslot and the uplink timeslots. Open loop control is often effectiveat pedestrian speeds as well as at higher speeds if the uplink slots areplaced close in time to the beacon. At high mobile speeds, it is likelythat power control performance will be improved if beacon RSCP filteringis enabled at the UE. The UE is responsible for detecting whether or notfiltering should be applied to the open loop component. Automaticdetection of the channel speed may be performed by the UE in order tocontrol the enabling of RSCP filtering. In some embodiments of thepresent invention, a UE disables a combined open loop/closed loop schemeoperating in accordance with the present invention when a UE passes athreshold value indicative of mobile speed.

Simulations have been performed to illustrate the performance advantagesof some embodiments of the present invention. The radio channelsimulated here represents an ITU indoor to outdoor and pedestrian modelB channel as described in ITU-R M. 1225 Guidelines for Evaluation ofRadio Transmission Technologies for IMT-2000. The outer loop SNIR targetwas based upon a 1% error rate. A residual SNIR error term observed atthe base station was monitored.

FIGS. 5A, 5B and 5C each illustrate a simulated probability densityfunction of the received SNIR in the network. In each of thesimulations, approximately 10,000 received SNIR values are sampled.Simulation results for each scenario are grouped and collected intobins. The vertical axis shows a number of occurrences for a particularrange (bin) of received SNIR values. A sampled received SNIR value thatfall within a range defined by a bin is counted as an occurrence forthat bin.

FIG. 5A shows simulation results for a system using only an open loopscheme. In this plot, the bin width is approximately 0.42 dB. Thesimulation results show a system good at tracking fast fading in thechannel, but not as able to track the interference variations includedin the simulation. These values are only updated at the UE viasignalling every 160 ms. As such, the error term shows considerablevariance at the receiver.

FIG. 5B shows simulation results for a system using only a closed loopscheme. In this plot, the bin width is approximately 0.48 dB. Thesimulation results show a system better able to track the interferencechanges, but not as able to track the path loss due to being limited inresponse to the TPC command +/−1 dB step size.

FIG. 5C shows simulation results for a system combining aspects of bothopen and closed loop schemes (as shown in FIG. 4). In this plot, the binwidth is approximately 0.24 dB. The simulation results show a systemable to respond to both path loss and interference changes.Additionally, the residual SNIR error term shows less variance. The plotshows that the variance of this distribution is considerably reduced forthe combined power control scheme.

For the above simulations (using the same fading and interferenceprofiles for each loop method), the following mean transmit powers wereobtained:

TABLE 1 Performance of Power Control Schemes Power Control Method MeanTransmit Power for 1% BLER Open Loop: (FIG. 2) 5.76 dB Closed Loop:(FIG. 3) 5.48 dB Combined Loops: (FIG. 4) 3.59 dB

For the simulated channel and interference scenario, the combined schemeis able to maintain a 1% block error rate (BLER) using 2.17 dB lesspower than the open loop scheme and 1.89 dB less power than the closedloop scheme. In a real system, this power saving may equate to greatercell coverage, higher uplink capacity and throughput, and increasedbattery life. The magnitude of the gains may change with differentchannel speeds, types and interference profiles but the performance ofthe combined should be better than both the open loop and closed loopschemes when used individually.

In terms of signalling overhead, the combined scheme helps to avoid aneed to signal SNIR Target and interference levels on downlink channels,and has a similar signalling efficiency as the closed loop scheme. Insome embodiments, the signalling efficiency is 1 bit per update.

In a system using the combined power control scheme, a new physicalchannel on the downlink may be used to carry fast allocation andscheduling information to a user, thereby informing the UE of the uplinkresources that it may use. This new physical channel could also be usedas the feedback channel for the combined power control scheme. Forexample, an allocation/scheduling channel could carry TPC commands.Alternatively, the combined scheme may be applied to existing channeltypes (dedicated or shared uplink physical channels) for UTRA TDD aswell as to other TDD systems.

Some embodiments of the present invention control uplink power levelsand may be incorporated into a UE with supporting features incorporatedinto a base station. For example, a Node-B or RNC may be implementedwith a new parameter, either included in a signalling command or abroadcast message, where the new parameter instructs a UE to enable ordisable the setting of uplink transmit power level based on both thepath loss estimation and the TPC commands. A parameter may indicatewhether a UE is to use open loop power control, closed loop powercontrol or a combined scheme.

Some embodiments of the present invention operate with a downlink signalincluding both a TPC command and an indication of the downlink transmitpower level. In these embodiments, the downlink signal provides bothdownlinks 416 and 430 (FIG. 4) in one signal. A UE may receive onephysical channel that it decodes for TPC commands, decodes for downlinkpower level indications, and measures for received power levels. Inthese embodiments, the UE measures a power level of a received signal,receives a TPC command, and calculates a transmit power level based onthe power level of the received signal and the TPC command.

While the invention has been described in terms of particularembodiments and illustrative figures, those of ordinary skill in the artwill recognize that the invention is not limited to the embodiments orfigures described. For example, the combined uplink power control schemedescribed above may be implemented a mirror image for controllingdownlink power. In this case, functions performed by the UE for acombined uplink scheme may be performed by the network. Similarly,functions performed by the network for the combined uplink scheme may beperformed by the UE.

The figures provided are merely representational and may not be drawn toscale. Certain proportions thereof may be exaggerated, while others maybe minimized. The figures are intended to illustrate variousimplementations of the invention that can be understood andappropriately carried out by those of ordinary skill in the art.

Therefore, it should be understood that the invention can be practicedwith modification and alteration within the spirit and scope of theappended claims. The description is not intended to be exhaustive or tolimit the invention to the precise form disclosed. It should beunderstood that the invention can be practiced with modification andalteration and that the invention be limited only by the claims and theequivalents thereof.

What is claimed is:
 1. A user equipment (UE) comprising: a transmitter;a receiver; and a processor operatively coupled to the transmitter andthe receiver, wherein the processor is configured to cause: the receiverto receive, from a network device, an indication that transmit powercontrol (TPC) command accumulation is enabled, the receiver to receive,from the network device, on a single physical channel, schedulinginformation and power control information that includes a multi-levelTPC command, and the transmitter to transmit, to the network device, anuplink signal based on the received scheduling information and themulti-level TPC command.
 2. The UE of claim 1, wherein the multi-levelTPC command includes a value selected from a plurality of pre-definedvalues.
 3. The UE of claim 1, wherein the transmitter is furtherconfigured to transmit the uplink signal on an uplink shared channel. 4.The UE of claim 1, wherein the network device is one of a Node-B or abase station.
 5. The UE of claim 1, wherein the multi-level TPC commandincludes a set of values that includes at least two values up or atleast two values down.
 6. The UE of claim 1, wherein the network devicegenerates the multi-level TPC command by comparing a measuredsignal-to-noise-plus-interference ratio (SNIR) with an SNIR targetvalue.
 7. The UE of claim 6, wherein the network device generates theSNIR target value based on an error metric of the uplink signal.
 8. TheUE of claim 1, wherein an interference measurement table stored in thenetwork device is updated based on an uplink interference value measuredfrom the uplink signal.
 9. The UE of claim 8, wherein the processor isfurther configured to cause the receiver to receive interferencemeasurements from the interference measurement table stored in thenetwork device.
 10. The UE of claim 1, wherein the processor is furtherconfigured to cause the receiver to receive an indication of a beaconpower level from the network device.
 11. A method performed by a userequipment (UE) having a transmitter and a receiver, the methodcomprising: receiving, by the UE, an indication from a network devicethat transmit power control (TPC) command accumulation is enabled;receiving, by the UE on a single physical channel from the networkdevice, scheduling information and power control information thatincludes a multi-level TPC command; and transmitting, by the UE to thenetwork device, an uplink signal based on the received schedulinginformation and the multi-level TPC command.
 12. The method of claim 11,wherein the multi-level TPC command includes a value selected from aplurality of pre-defined values.
 13. The method of claim 11, whereintransmitting the uplink signal includes transmitting the uplink signalon an uplink shared channel.
 14. The method of claim 11, wherein thenetwork device is one of a Node-B or a base station.
 15. The method ofclaim 11, wherein the multi-level TPC command includes a set of valuesthat includes at least two values up or at least two values down. 16.The method of claim 11, wherein the network device generates themulti-level TPC command by comparing a measuredsignal-to-noise-plus-interference ratio (SNIR) with an SNIR targetvalue.
 17. The method of claim 16, wherein the network device generatesthe SNIR target value based on an error metric of the uplink signal. 18.The method of claim 11, wherein an interference measurement table in thenetwork device is updated based on an uplink interference value measuredfrom the uplink signal.
 19. The method of claim 18, further comprising:receiving, by the UE, interference measurements from the interferencemeasurement table stored in the network device.
 20. The method of claim11, further comprising: receiving, by the UE, an indication of a beaconpower level from the network device.